1. Field of the Invention
The present invention relates to a semiconductor apparatus, an exposing apparatus, and an image forming apparatus, and may be advantageously applied to a print head in which a plurality of light emitting element array chips are aligned on a circuit board.
2. Description of the Related Art
A conventional light emitting diode (LED) print head, which is used in an LED printer, employs a configuration in which a plurality of semiconductor light emitting element array chips are mounted on a print wiring board and are aligned in a straight line. Each array chip has a plurality of light emitting portions formed in its surface, the light emitting portions being aligned in one dimension at predetermined intervals.
This type of LED print head is assembled by first applying an adhesive to a print wiring board, and then semiconductor light emitting element array chips are pressed on the adhesive against the print wiring board, and finally allowing the adhesive to cure. In this manner, the semiconductor light emitting element array chips secured on the print wiring board.
If the space between adjacent chips is too narrow, the adhesive is drawn into the space by capillary action up to the same level as the surface of the array chips, soiling the light emitting portions and causing usable light power to decrease. The adhesive may also contaminate the wire bonding pads formed on the end portion of the surface of the array chips, reducing the mechanical strength of the wire bonded portions.
Japanese Patent Laid-Open No. 2011-131475 discloses a print head in which the adhesive is applied only to a limited surface area on the print wiring board, e.g., a middle portion of the back surface of the array chip, thereby preventing the adhesive from being drawn into the space between adjacent array chips up to the upper surface of the array chips.
However, applying the adhesive only to a middle portion of the back surface of the array chip causes end portions of the back surface to be uplifted, so that edges of the array chip may be chipped during wire bonding or the array chip may be inclined at an angle with respect to the surface of the print wiring board.
If end portions of the back surface of the array chip are uplifted from the print wiring board, heat dissipation is more difficult at the end portions than in the middle portion of the back surface, so that the temperature of the end portions is higher than the middle portion.
Although applying the adhesive only to a limited portion of the back surface is effective in preventing the adhesive from contaminating the chip surface, but may increase the chances of the chips inclining and being damaged, impairing the reliability of the LED print head.